The present invention is related to a telescopic tube of an upper beam of a vertical type Venetian blind, comprising a major/minor telescopic upper beam, two rows of sliding clamp blocks, two linkage actuated members, and two guide straps wherein the major/minor telescopic upper beam has opposite grooved guide tracks disposed at the open bottom side thereon for the guide straps to be adapted therein, and the sliding clamp blocks are serially connected into rows via X-shaped linking bars; whereby, when the two rows of the sliding clamp blocks are activated by the X-shaped linking bars thereof, clamping parts of the sliding clamp blocks disposed at the front section of each row thereof are sequentially displayed at a movement slot of the linkage actuated member therein till a clamping part located at a retaining hole of an adjustment block therein is pulled to activate the linkage actuated member which is then moved smoothly forwards therewith along the guide straps at the grooved guide tracks therein, forming pulling force synchronically at both the front and middle sections thereof to equidistantly display the sliding clamp blocks with blades attached at the clamping parts thereof so as to achieve the overall beauty as well as the best sheltering effect of the vertical type Venetian blind thereof.
Please refer to FIG. 1. A conventional telescopic tube of an upper beam of a vertical type Venetian blind is made up of an inverted U-shaped major/minor telescopic upper beam 10, sliding clamp blocks 12 serially connected into two rows via a plurality of X-shaped linking bars 11 to be adapted at both inner side of the telescopic upper beam 10 thereof respectively. Each sliding clamp block 12 has a protruded part 122 disposed at the top thereof, two cord passages 121 disposed at the protruded part 122 thereon for pull cords 13 to be led there-through respectively, and a clamping part 124 extending downwards at the bottom thereof. Two major/minor telescopic adjusting rods 14 are respectively led through symmetrical adjusting holes 123 disposed at both lateral sides of the sliding clamp block 12 thereon. And a rotary gearing rod works with a helical gearing to adjust the angle of blades 15 attached to the clamping parts 124 of the sliding clamp blocks 12 thereof. Via the pull cords 13 matching to the X-shaped linking bars 11 thereof, the two rows of sliding clamp blocks 12 in linkage connection are activated to move at the major/minor telescopic upper beam 10 therein via rollers 125 sliding along the grooved guide tracks 101 symmetrically disposed at the open bottom side of the major/minor telescopic upper beam 10 thereof as shown in FIG. 2. Besides, the major/minor telescopic upper beam 10 can be properly adjusted to fit into windows of different width.
There are some drawbacks to such conventional telescopic tube of an upper beam of a vertical type Venetian blind. First, to display the vertical type Venetian blind thereof as shown in FIG. 1, the X-shaped linking bars 11 are drawn from the corresponding inner side thereof, activating the sliding clamp blocks 12 to unfold in a sequence therewith. The X-shaped linking bars 11 disposed at the front section thereof must be fully extended before the linking bars 11 disposed at the rear section are actuated to move forwards therewith, which may result in the incomplete display of the linking bars 11 at the rear section thereof. Thus, the blades 15 attached at the clamping parts 124 of the sliding clamp blocks 12 can't be equidistantly unfolded in display, which not only mars the overall beauty of the vertical type Venetian blind, but also fails to provide the best sheltering effect thereof. Second, due to the design of the major/minor telescopic upper beam 10 thereof, a step-wise flange 102 is produced at the joint of the grooved guide tracks 101 of the major/minor telescopic upper beam 10 thereof, which may unevenly hinder or stop the rollers 125 thereof in movement as shown in FIG. 2. Thus, pulling force must be instantly applied to release the rollers 125 from the step-wise flange 102 thereof for them to continue the movement thereof, which is quite inconvenient in practical use.